This invention pertains to remote supervising apparatus and more particularly to apparatus for remotely supervising devices via a telephone line.
There have been proposed numerous methods and apparatus for controlling via a telephone line electrical contacts or the like installed at a remote location. These contacts can be used to start or stop, for instance, equipment, air-conditioners, lighting, etc. In order to avoid unauthorized or inadvertent operation of such devices it has been suggested that the user place two sequential calls with a time interval between such calls. The receiving equipment is designed to react only for that time interval. Along the same lines there has been suggested the placing of two calls with each call being terminated after a predetermined number of ring signals. In this way it is possible to provide a two-digit number which can be recognized by electronic or electromechanical equipment at the remote location. However, these methods and apparatus require that the ring signals the caller hears be synchronized with the ones that are actually sent out by the remote control equipment. Since this is not always true, such a method becomes useless. In addition, both of these methods suffer from a very serious drawback apart from being both impractical and time consuming. In particular since the telephone calls only result in unanswered ring signals, there is no base for charging the use of a telephone circuit being provided by the telephone company. Hence, such equipment would not be permitted to be attached to the public telephone network controlled by the telephone companies.
There is also known a solution to the problem which does not suffer from the above-mentioned drawbacks. In such a system the ring signal initiates the operation of a motor driven timing device which is programmed to permit the ring signals to continue for 30 seconds. At the end of that time, a low resistance is connected to the line causing the ring signal to stop. At the same time information is provided to the telephone station for billing purposes. During the following 30 seconds the caller hears nothing and it is expected that an accidental or unauthorized call will hand up during that period. At the end of that period the timing devices operates the relay which performs the desired operation and sends a confirming signal back. However, no supervision is provided and it takes a considerable time to complete just one maneuver. Therefore, if a caller should leave his phone off the hook an undesired operation takes place.
Finally, there has been proposed in U.S. Pat. No. 3,049,592 a method for controlling terminal equipment utilizing stepping relays and requiring the transmission of combinations of signals and no-signals to effect the control. Not only is the apparatus for this system expensive and complicated but the actual procedures required of the user lend themselves readily to errors.